We have discovered with the Wide Field Cameras on board
BeppoSAX the weak transient X-ray source SAX J2239.3+6116 whose
position coincides with that of 4U 2238+60/3A 2237+608 and
is close to that of the fast transient AT 2238+60 and the
unidentified EGRET source 3EG 2227+6122. The data suggest that
the source exhibits outbursts that last for a few weeks and peak to a
flux of
erg cm-2 s-1
(2-10 keV) at maximum. During the peak the X-ray spectrum is hard
with a photon index of . Follow-up
observations with the Narrow-Field Instruments on the same platform
revealed a quiescent emission level that is 103 times less.
Searches through the data archive of the All-Sky Monitor on RXTE
result in the recognition of five outbursts in total from this source
during 1996-1999, with a regular interval time of 262 days.
Optical observations with the KPNO 2.1 m telescope provide a
likely optical counterpart. It is a B0 V to B2 III star with
broadened emission lines at an approximate distance of 4.4 kpc.
The distance implies a 2-10 keV luminosity in the range from
to
erg s-1. The
evidence suggests that SAX J2239.3+6116 is a Be X-ray binary with an
orbital period of 262 days.